Doub1e-strand breaks (DSBs) in DNA result from endogenous and exogenous insults. Failure to properly repair DSBs can result in chromosome fragmentation, translocation, or deletion, often resulting in carcinogenesis. The long-range goal of these studies is to understand how the recombinational repair machinery contends with chromatin structure. The focus of this proposal is RAD54, which plays a key role in the repair of DSBs in yeast, mice, and humans. RAD54 is a member of the SWI2/SNF2 family of DNA-stimulated ATPases, and has been proposed to facilitate repair of double strand breaks by disrupting chromatin structure. Aim 1 of this proposal will use chromatin immunoprecipitation to analyze the recruitment of RAD54 to an induced DSB. Rad mutant strains will be used to identify the network of factors required by RAD54. Aim 2 will determine whether RAD54 is a subunit of a protein complex using co-immunoprecipitation of tagged subunits. Aim 3 will test whether RAD54 is a chromatin-remodeling enzyme. Although these initial studies will be carried out in a simple eukaryote, I anticipate that the results will be applicable to mechanisms of DSB repair in all organisms, and that these studies will help to further the analysis of human DSB repair machinery.